The Syrian government has stepped up its offensive against opposition activists ahead of a planned ceasefire, with the fresh hostilities prompting an influx of refugees into neighbouring Turkey, activists and the Turkish government have said.

With fighting escalating in several locations across the country, the stream of Syrians fleeing into southern Turkey has increased, with about 2,500 crossing over on Thursday alone, Ahmet Davutoglu, the Turkish foreign minister said.

The movement of people comes as as Kofi Annan, the joint envoy of the UN and Arab League charged with resolving the crisis, said that both the government and opposition's fighters must cease all hostilities by 6:00am local time (3:00am GMT) on April 12 in order to comply with his six-point peace plan.

Davutoglu said that about one-third of the 24,000 Syrian refugees currently in the country had arrived in the last two weeks.

Turkey has been receiving refugees since the beginning of the now year-long uprising against Syrian President Bashar al-Assad's government.

Davutoglu told UN Secretary-General Ban Ki-moon on Friday that his country would seek UN assistance if the influx continues.

Turkey has in the past floated the idea of creating a small buffer zone inside Syria if refugee flows become overwhelming.

"These developments are seriously worrying us," Davutoglu said of the intensifying violence.

The new refugees are crossing into the Turkish village of Bukulmez, a Turkish official said, and being transported to a camp at Reyhanli.

"The army is destroying buildings and bombing them till they turn to charcoal," said Mohammed Khatib, a refugee who said he came from Kastanaz, a Syrian town of 20,000 people.

Thousands of Syrians have also fled to Lebanon and Jordan since the uprising began. An estimated total 50,000 to 60,000 have left the country.

The apparent trigger for the fresh wave of refugees is a renewed assault on the Syrian town of Idlib, in the country's northwest, by the Syrian army.

Anti-Assad activists say that scores have been killed in the village of Taftanaz, and that the nearby vilalge of Killi was being shelled on Friday.

"Helicopters and tanks are bombarding continuously. Taftanaz has been burnt to the ground for three days."

Turkey's state broadcaster showed images of dozens of Syrians waiting by the Turkish border, hoping to cross over.

Violence rages

In the central Syrian city of Homs, meanwhile, thick black smoke billowed from a residential area on Friday and sounds of heavy gunfire and explosions could be heard, the AP news agency said.

Government forces have also targeted the town of Rastan, just north of Homs, with heavy machine-guns and mortars, the Syrian Observatory for Human Rights (SOHR) said on Friday.

Ground troops are said to have entered the city and clashed with opposition fighters, the UK-based rights group said.

Rastan has been under siege by the government's forces since late January.

Government forces also broadened an offensive in the Damascus suburbs of Douma, Saqba, Arbeen and Dumair, exchanging fire with rebels, activists said.

In Douma, activists said snipers had set up positions and that tanks were patrolling the town's streets. Activists also reported shelling in the town.

The SOHR said that at least 24 Syrians had been killed in violence across the country on Friday.

It said that at least 10 people had died in shelling, including four rebel fighters, in Homs.

Two soldiers were killed in separate clashes, and one person was killed in Douma, the group said.

It also reported that seven civilians and four soldiers had been killed in clashes and bombardment in Anadan, north of Aleppo.

Fresh protests

Also on Friday, tens of thousands of protesters marched in towns across the country, calling for Assad to step down, the SOHR and other activist groups said.

In the central province of Hama, troops opened fire on demonstrators, wounding three people, the SOHR said.

MWC News cannot independently verify accounts of the violence because of reporting restrictions imposed by the Syrian government.

Assad's government blames the violence on "armed terrorist gangs" and, on Friday, the Syain state news agency said that a message had been sent to the UN's Ban telling the UN that "terrorist acts" are on the rise in the country.

The message said the number of soldiers and security agents killed since mid-March last year had risen to 2,088, and that more than 478 police officers had also died.

Annan has said the Syrian army must also have withdrawn from all towns and cities and cease the use of heavy weapons 48 hours prior to that deadline, as it has previously agreed to do.

He told the UN General Assembly by video link from Geneva on Thursday that the Syrian authorities had told him this week troop withdrawals were under way in the towns of Deraa, Idlib and Zabadani.

But he said he wanted "fuller information".

Meanwhile, Norwegian Major-General Robert Mood is due to hold talks with officials in Syria regarding the possibility of a UN monitoring force being set up to enforce the ceasefire. The force would have between 200 and 250 members.

The deployment of monitors would have to be authorised by the 15-member UN Security Council.